This invention relates to a synchrotron radiation (SR) source and a method of making the same, and more particularly relates to an SR source of the type having a beam absorber for absorbing SR beams provided in a charged particle beam duct of a charged particle beam bending section and a method of making the same.
The orbit of a charged particle beam is deflected inside the charged particle beam duct of the bending section to cause the charged particle beam to radiate an SR beam and the interior of the charged particle beam duct must be maintained in a vacuum condition to minimize the loss of charged particles due to its collision with other different particles.
However, when the SR beam directly irradiates the wall of the charged particle beam duct, the irradiated portion, conventionally made of stainless steel or aluminum alloy, undergoes a photo-excited reaction to discharge a large amount of gas and as a result the interior of the charged particle beam duct can not be maintained in a high vacuum condition.
The amount of discharged gas is very large, measuring 10 times to 100 times the amount of gas outgoing merely owing to thermal desorption. It has been envisioned to suppress the gas discharge by providing a beam absorber at a portion, where the SR is irradiated, of the interior wall of the charged particle beam duct. More specifically, the beam absorber is made of a material which has a low photo-excited gas discharge coefficient so that the amount of gas discharged from the surface and interior of the material by a photo-excited reaction concomitant with SR irradiation is small, the beam absorber being used to suppress the generation of gas. Conventionally, as discussed in IEEE, Transactions on Nuclear Science Vol. NS-32, NO. 5, Oct. 1985, pp. 3354-3358, a beam absorber having a linear or approximately linear form is mounted in a charged particle beam duct by being inserted thereinto through an insertion port dedicated to the beam absorber and which is formed in the outer circumstantial wall of the charged particle beam duct.
The mount structure for the beam absorber described in the above literature is well adapted for relatively large-scale SR sources in which the radius of curvature of the charged particle beam duct of the charged particle beam bending section is large and sufficient room is provided.
The prior art pertains therefore to technology of large-scale SR sources and fails to take small-scale SR courses into account.
Should the conventional mount structure for the linear or approximately linear beam absorber be applied to small-scale SR sources in which the radius of curvature of a bending section is small, the curvature of a charged particle beam duct of the bending section is large and the linear beam absorber could not cover or profile the overall circumference of the bending section of large curvature, with the result that there remain portions on the interior wall of the charged particle beam duct which are irradiated directly with the SR. To solve this problem, a number of insertion ports dedicated to beam absorbers have to be provided over the overall circumference of the bending section. However, because of the need to provide the bending section with SR beam lines for guiding SR beams, there is almost no room for the provision of dedicated insertion ports over the overall circumference of the bending section.
Accordingly, the conventional mount structure for the linear beam absorber is totally unsuited for application to small-scale SR sources.